Electronically Induced Proton Transfer Reactions in Salicylic Acid Esters and Salicyloyl Chloride

Article abstract of DOI:10.1021/j100228a024

The multiple fluorescence emission spectra, excitation spectra, and lifetime of isopropyl salicylate, tert-butyl salycilate, and salicyloyl chloride have been analyzed in the gas phase and in cyclohexane and N,N-dimethylformamide solutions.Study of the electronic emission and IR absorption spectra of both esters and methyl salicylate gives further support to the hypothesis of a ground-state equilibrium between two intramolecular H-bonded conformers.The efficiency of the excited-state proton transfer reaction was determined from fluorescence and lifetime data of the 450-nm emission and found to be ca. 40percent lower in tert-butyl than in methyl salicylate.On the other hand, the characteristic fast electronic energy relaxation of these compounds was not sensitive to the carboxyl substituent.Finally, the effect of solvent polarity on the radiationless rate was discussed in terms of the interaction between (?,?^*) and (n,?^*) states of the zwitterionic structures.